The invention relates to pumps and more particularly, but not exclusively, to pumps of the type comprising an externally toothed or lobed inner rotor mounted eccentrically within and meshing with an internally toothed or lobed rotor. One pump of this type comprises a lobed inner rotor which rotates eccentrically within an outer rotor having one more lobe than the inner rotor, the inner and outer rotors making permanent sliding contact at points spaced around their periphery and defining sealed spaces which decrease in volume between fixed inlet and outlet ports.
Pumps of this type are often used as oil pumps in internal combustion engines. The pump rotors are generally mounted in a housing, part of which may be constituted by a pocket in the engine block, and a driving shaft projects into the housing to drive the inner rotor which in turn drives the outer rotor.
According to the present invention there is provided a pump comprising a housing, pumping elements mounted within the housing for pumping fluid from an inlet to a main outlet. The main outlet communicates with a secondary outlet by way of a control gap which filters the fluid passing into the secondary outlet.
In preferred arrangements, the housing comprises a body portion and a cover plate. The body portion is formed so as to define the inlet and outlets and provides a wall to define with the outer rotor, the control gap between the main and secondary outlets.
It is a preferred feature that the secondary outlet has an orifice through which filtered fluid can flow. Ideally the orifice is connected to external tubing to direct the filtered fluid to predetermined locations.
In certain embodiments, the pumping elements comprise an externally toothed or lobed inner rotor mounted eccentrically within and meshing with an internally toothed or lobed outer rotor which is mounted for rotation within and relative to the housing. Conveniently, the inner rotor is adapted to be driven in rotation, the rotation causing rotation of the outer rotor.